en.javascript.info/1-js/4-data-structures/4-object-for-in/1-is-empty/solution.md

//+ run
function isEmpty(obj) { 
  for(var key in obj) {
    return false;
  }
  return true;
}

var schedule = {};

alert( isEmpty( schedule ) ); // true

schedule["8:30"] = "подъём";

alert( isEmpty( schedule ) ); // false